why select * from return only the first field?

I'm making the next query to the db

$result = $con->query ( 'select * from table');
$datos = $result->fetch_assoc();
echo "Cantidad de datos: ".count($datos).",";
print_r($datos);

Should show an array with all the entries, but only show the first entry. Why?

PS: i saw other posts but i haven't limit or joins.